Muffler



March 17, 1936. L R HEATH 2,034,186

MUFFLER Filed Oct, 15, 1952 Patented Miu'.v 17, 1936l UNITED STATESPATENT OFFICE MUFFLER Laurence R. Heath, Arlington," Mass. ApplicationOctober 15, 1932, Serial No. 637,946

13 Claims.

'I'his invention relates to improvements in mufilers of the' typecommonly employed for silencing noises resulting from the discharge ofexhaust gases from an internal combustion engine. The objects of thisinvention are to provide a muiiler of this kind of improvedconstruction, by means of which the back pressure caused by the muilleris materially less than in muiiiers heretofore commonly employed; alsoto provide a muiiler of this kind in which the pulsations in thepressure and flow of exhaust gases are reduced to such' an extent that asubstantially uniform or only slightly pulsating flow of exhaust gas isdischarged from the muffler; also to provide a mumer of this kind inwhich the pulsating gases entering the muiiler are permitted to expandin certain chambers formed about the mumer and to again join the currentof gas going through the muiller during low pressure intervals orbetween the pulsations; also to pro vide a mufiier of this kind in whichnoise due to the exhaust is reduced by producing a substantially uniformflow of exhaust gas through the discharge passage of the muiller; alsoto produce a muilier of this kind inlwhich the chambers surrounding theinner passage through the muiiler are designed to permit gases to ilowback and forth into and out of the chambers in accordance with thepulsations of the gas in the inner passage, and also to cause some gasto ow through the chambers fromthe inlet to the discharge of themuiller; also to improve muiilers of this kind in other respectshereinafter specifled.

I have found that when a muiiler is designed in i such a manner as tosmooth out the pulsating flow of the exhaust gases from an internalcombustion engine, such a muiiler will at the same time remove theobjectionable exhaust noises. Even the simplest types of muiliers of thekind heretofore employed will transmit very little of the initial soundof the exhaust of an engine, but in such muillers the waves of gasesleaving the mufliers create noises or sounds which are objectlonable.`In accordance with my invention,

I, therefore, reduce the intensity of the pulsations of the exhaustgases, and I have found -that when a muffler is designed to remove thesepressure or flow pulsations `:from the exhaust gases, the objectionablenoise of the exhaust is f also eliminated. The muillers shown in theaccompanying drawing are, therefore, designed to remove the crests fromthe impulse waves of exhaust gases entering the muiiler and to em- 55'ploy the gas from these crests to fill up subsequent troughs or lowpressure -spaces between these waves. thus producing a flow oi' gas atthe discharge end of the mumer which has very lit- Wf'tleevanationwinpressure. I have alsoaccom# 00 plished this by producing a niumer havingva passage extending straight through the same so that the gases passingthrough the muiiler encounter a minimum resistance to ilow and,consequently, result in very little back pressure."

In the accompanying drawing, I 'have illus- 5 trated some forms ofmuiliers capable of producing the desiredl results, but it will beunderstood that the muillers shown in the drawing are merelyillustrative, since Wide variations in the numbers of baiiles and in thepassage of gases l0 through shells may be made in order to accommodatemuiilers to engines of diierent kinds. In this drawing:

Fig. 1 represents a longitudinal sectional elevationfof a mufflerembodying this invention. l5

Figs. 2, 3 and 4 are similar sectional elevations of muiers of modifiedconstructions.

Fig. 5 is a transverse sectional elevation on line 5-5, Fig. 2.

Fig. 1 embodies the simplest form of my in- 20 Vention and in this form,the muiller is provided with an outer shell I0 having heads II and I2secured to the ends thereof, the head I I at the inlet side of themuffler Abeing provided with a tubular extension I 4 constituting theinlet of the 25 muiiler and with which the exhaust pipe from the enginemay connect, and the head I2 at the discharge end of the muierbeingformed with a tubular extension I5 to which a tail pipe may be secured.The heads II and I2 may also be 30 provided with shoulders with which anintermediate shell I6 engages. The muffler also has an inner shell orconduit I'I which may be suitably mounted on the muiiler in any desiredmanner,

` and which, in the construction shown, is sup- 35 ported on the innershell4 by means of baiiies I8 and I9. A ny other means for supportingthe shells and heads relatively to each other may be provided.

In accordance with my invention, the inner 4o tube or shell Il ispreferably constructed to pass theflow of 'exhaust gas therethrough, andthe discharge end of this tube or shell may be made slightly smallerthan the inlet opening. In the particular construction shown in Fig. l,this 45 result is obtained by constructing the inner shell so vthat thesame tapers slightly from the receiving end thereof to the dischargeend. This causes the gases entering the muler from the inlet openingtherein to build up a pressure near 50 the inlet end of the inner shellI1 which is slightly greater than the pressure at the discharge end ofthis shell.

In accordance with my invention. this shell is made of perforated metalsubstantially throughout the length thereof. 'I'he perforation;

may be of any suitable or desired form, but I 2 obtained, and that awhistling sound which sometimes results if perforations of circularshape are used, does not occur. While such rectangular perforations arepreferably employed, it will be understood that perforations ofany otherform may be used, since the object of these perforations is mainly topermit gases to pass out of the inner. shell through these perforationsinto a chamber 22 formed between the inner and intermediate shells ofthe mufiier. In the construction illustrated in Fig. 1, apertures 23 areformed in the intermediate shell near the inlet end of the muiiler sothat gases may pass through these apertures 23 into the outer chamber 24of the muliler which is arranged between the intermediate and outershells thereof. The inter` mediate shell is provided with a secondseries of apertures or openings 25 which, in the particularconstructions shown, are arrangedin rear ofa the baiiie I9, and thedischargevend of the inner shell terminates -at a distance' from thedischarge duct I of the muier so that the discharge end of the shell I1has an ejector action which tends to draw gases through the apertures 25to mix With the gases discharged from the innershell, and thus to enterinto the tail pipe of the muiiier. The discharge end of th inner shellextending beyond the baiiie I9 is preferably not perforated, to increasethe ejector action. Y

In the operation of this muffler, when a charge of exhaust gas entersinto the inner shell I'i thereof, asa result of the opening of anexhaust valve of the engine, the pressure wave orpulsation of this gaswill have a relatively high peak caused by the' gas leaving the engineat considerable pressure immediately after the opening of the exhaustvalve. 'Ihis wave or pulsation of exhaust gas entering into the innershell Il will, of course, tend to expand as rapidly as possible and uponreaching the inner (shell, thisK gas will immediately expand through theperforations 20 therein and enter into the inner chamber 22. Because ofthe high pressure peak, some of the gas enteringvthechamber 22 willimmediately ow through the apertures 23 into the outer chamber 24.Immediately after the peak of the wave, there will be a depression inthewave or pulsation, so that gases in the chambers' 22 and .24 will againtend to flow in the reverse direction through the apertures 22 of theinner shell I1, thus adding this amount of gas to the trough ordepression of; the pulsation. It will be evident, therefore, that byremoving the peak of a wave or pulsation of exhaust gas and againreturning the gas Aof the peak thus removed into the trough, both thepeak and the depression or .trough of the waveor pulsation have beenremoved, so that when this exhaust gas nally enters'the tail pipe, itwill iow at a fairly uniform rate and with greatly reduced variation inpressurev between the peak and the trough of the wave of exhaust gas.uniform ow orJ discharge of the gas fromx the tail pipe into the air,consequently, takes place Without the. objectionable from the innershell also have a silencing effect f upon sound waves in the muierbecause of the refraction of these sound waves in passing through gasesof diierent temperatures.

It will bek understood that the apertures 25, which, in the constructionshown, are arranged in rear of the bale I9, may be located in front ofthis baille, in which case, the ejector action will be replaced by adrawing of gas throughthese apertures due to the fact that the pressureof gas at the discharge end of the inner shell IT, due to the taper ofthisshell, is .less than at the inlet end thereof. In either case, coolgas will iiow crosswise of the inner-shell resulting in the well knownsilencing effect upon sound waves. f

The operation of 'this muler is believed to be as follows: Whena wave orpulsation of gas enters into the inlet end, gas flows rapidly outthrough the perforations in the inner shell into the intermediate spaceor chamber of the mufer located between the inner and intermediateshells, and a portion of this gas flows through the apertures 23 intothe outer chamber of the muiiier. Immediately reduction of the pressurein the inner shell results, and when the pressure wave or pulsationreaches the discharge end of the muflier, its pressure is so reducedthat no objectionable sound results when this pulsation is discharged'from the end of the tail pipe.` A considerable portion of the gas fromthe intermediate and outer shells will flow back into the inner shellwhen the peak of the pressure wave has passed and will then passoutwardly through the tail pipe in a comparatively steady or uniformflow, and without producing objectionable noise. By this construction,the flow of gas from the inner shell during the peak or high pressureportion of the pressure wave, reduces or flattens out this `peakand-materially reduces the pressure in the inner shell, and when thetrough or portion of low pressure of the. wave passes. into the innershell, this gas in the intermediate and outer chambers is returned andlls in this trough, -with the result that afairly uniform discharge ofgas takes place through the discharge end of the muilier.

In addition to this alternating -movement of gas in the chambers of thismuiiler, there will also be a movement in the outer chamber toward v thedischarge end of the muilier, this movement being produced b y theejector action of the discharge end of the muier, resulting 'in themixing ofgases of different temperatures. which has been described.Probably a similar movement of gas takes place inthe inner chamberbecause of the fact 'that the pressure in the inner shell is greater atthe inlet. end thereof than at the discharge end., 'I'his passage of gaslengthwise of the muiiierqthrough the chambers surround ing the innershell has a further equalizing eti'ect on the gas discharged from themufller, and also reduces back pressure by cooling the gases by contactwith the outer shell. thus reducing the volume of the gas to bedischarged. The resulting mixture of gases of varying temperaturesresults in a turbulence and refraction and absorption of sound waves.Furthermore, by maintaining a now of rgases through the severalchambers, a deposit and accumulation of other foreign material in thechambers is prevented.

tween the outer and intermediate shells intermediate of the heads of themuffler, and a pair of bailles 3| and 32 are provided between the innerand intermediate shells and spaced at intervals; This arrangement of thebailles 3| and 32 results in the formation of` chambers 35, 36 and 31between the inner and intermediate shells, and the baille 30 results inthe formation of outer chambers 384 and 39 between the outer andintermediate shells. The intermediate shell is provided near the inletend of the muiller with a plurality of apertures 48 through which gasespassing through the perforations of the inner shell into the chamber 35may pass into the chamber 38, and additional perforations 4 I, fewer innumber than the perforations 40, establish communication between thechamber 38 and the chamber 36. Similarly a relatively1 small number of4perforations 42 are provided in the intermediate shell between thebailles 30 and 32 to establish communication between the chamber 36 andthe chamber 39, and a larger number of perforations or apertures 43 areformed to establish communication between the chambers 39 and 31.

In the operation of this muiller, gas from the pealrs of the pulsationspasses out through the perforations of the inner shell and successivelyenters the chambers 35, 36 and 31. Gases from the chamber 35 may passthrough apertures 4U into the outer chamber 38, and when the trough ofthe pressure wave is reached, a part of these l gases may again pass inthe reverse direction through the openings 40 and perforations in theinner shell. Other gases from the outer chamber 38 will pass into theintermediate chamber 36 through the eapertures 4|, it being borne inmind that the pressures along the tapered inner shell vary, beinghighest at the inlet end of the muffier and lowest at the discharge end.Gases from the chamber 36 may also pass outwardly through the apertures42 into the chamber 39, and then through apertures 43 into the chamber31, and thence back to the inner shell. In this case, the

. inner shell does not have the ejector action described in connectionwith Fig. 1, but by slight l rearrangement of the` baille supporting thedis- 1 can be readily changed to charge end of the inner shell from theintermediate shell and the apertures 43, the muiller producethe ejectoracti/Jn, if the sameis desired.

In the construction shown in Fig.`2, in addition to the eiect ofproducing an evenl ilow of f gas through the muiller, the chamber'36 hasa decided silencing action on vsound waves because of the fact that hotand cold gases ilow into and out of this chamber and set up a turbulencein this chamber, which has been round to deaden sound. The muiller shownin Fig. 2 is of conshells shown in Figs. 1 and 2. Baines siderablylarger capacity than the one shown in Fig. 1, and-because oi theplurality oi chambers provided lengthwise of the inner shell, a greaterequalization of pressure is produced by this muiller, than by the oneshown in Fig. 1, which greater equalization would be necessary inconnection withiarger engines because of greater pressure variations ofthe exhaust gases. It will be obvious that the number of chambers in amuiiler can be readily varied as desired by in` creasing or decreasingthe number of bailles and the length of the shells, but preferably thechambers are so arranged that the gases passing lengthwise through thechambers about the inner shell will pass alternately from anintermediate chamber to an outer chamber and from such outer chamber toanother intermediate chamber located nearer to the discharge end of themuifier. 'This reversal of directions or alternate inward and outwardflow of gases helps materially in eliminating sound waves from the gasesdischarged by the muffler. It will, 'of course,'be understood that deadchambers, or chambers into and out of which gases flow only through thesame set of openings may'be used, if desired,

in connection with the interconnected chambers.

Fig. 3 shows a muffler which is quite similar to the one shown in Fig.1, except that in Fig. 3 the inner sleeve is formed of two parts ofdinerent diameters, the part of the smaller diameter being nearer thedischarge end of the muiller, and the two parts being held in place byshoulders formed on an intermediate head 46. The portion 41 of the innershell or tube is of larger diameter than the portion 48, so that therewill be a slightly greater pressure at the inlet end of the muiiler thanat the discharge end. The intermediate head 46 divides the chamberbetween the inner and intermediate shells into two intermediatechambers, and a similar intermediate head could, of course, be employedon the muiller shown in Fig. 1. This arrangement causes gases to passirom.one of these chambers through apertures 49 into the outer chamberbetween the -outer and intermediate shells and then through apertures 50from the outer chamber into the other intermediate chamber, and finallyback to the inner shell.

It will be noted that in all of the constructions shown, none Vof thechambers formed in the oi' the muiller in preventing corrosion orrusting of the same, and maintains the eiiiciency of the muiller at itshighest point throughout its life by preventing the filling up of anychamber with liquid, soot', or other foreign materiali. This mufiler canvbe readily changed to produce the ejector action by arranging theapertures 5.0 and the baille which supports the discharge end loi' theinner shell in lthe manner shown in Fig. 1, this change also beingpossible with the other constructions herein illustrated.

'I'he construction shown in Fig. 4 is intended for use where amaterially greater amount oi' silencing is required, than can beobtained from the use of the muiller shown in Fl'gs. 1 and 3, and inthis case, the inner shell comprises three sections or parts 55, 56 and51, which are of successively smaller diameters, and thus produce astepped arrangement in the inner shell which may be used interchangeablywith the tapering 4 vided between the irner and intermediate shells atthe ends of the several sections or parts of ythe inner shell, and anadditional baille 58 is provided intermediate of the ends of the section5l o f the inner shell. Bailies are also provided between theintermediate and theouter shells and arranged alternately with baiiiesbetween the inner and intermediate shells. This forms intermediatechambers or compartments 59, 60, 6| and 62 between the inner andintermediate shells, and 'outer chambers 63, 64 and 65 between theintermediate and outer shells. The apertures in the intermediateshellare so arranged that gases may pass from the intermediate chamber 59into the outer chamber 63 and through this chamber 63 into theintermediate chamber 60. In the chamber\60, the gases may Iiow eitherinto the intermediate shell or into the chamber 64 and gases cooled inthe outer chamber 63 will mix with the hot gases enteringy through theperforations of= the portion 56 of the inner shell, and thus produce theturbulence referred to in connection with the description of Fig. 2.,The presence of gases of diiierent temperatures in diierent parts ofthe chamber 60 produces refraction and absorpton of sound waves. Gasesfrom the chamber 64 enter into the' chamber 6I, and consequently,turbulence is again set up in this chamber with the result of furtherdeadening of sound waves. Some gases from the chamber 6I will enter intotheouter chamber 65, and thus into a chamber.

-62, this flow being induced by the decreased pressure at the dischargeend of the inner shell, or

' if desired, the baille and apertures at' the discharge end of theintermediate shell -may be rearranged as shown in Fig. 1, to produce anejector action.

It win be understood in connecten with autor these mufliers which havebeen described, that the iiow of gasesthrough the chambers about theinner shell is not necessarily continuous in -a direction from thereceiving to the discharge end of the muiiler, since this iiow varieswith varia,-v tions in pressure in the inner shell. For example,

when the peak of a pressure or pulsation wave of exhaust gas reaches theinner shell, there will be a very rapid ow of gas from the perforationsof the inner shell and a corresponding iiow into the chamber between theintermediate and outer shells. When the peak has passed, there will begreater pressure in the chambers surrounding the inner. shell than inthe inner shell, and consequently, there will-be an immediate return ofthe gases from the chambers to the inner shell. By the time the troughof the wave or pulsation is reachedfthe larger volumes or gastemporarily stored in the outer chambers of the muiiler will reach theinner shell,l the return of `these gases 'to the inner shell beingdelayed because .of the greater distance which they have to travel. Intlf-is manner, the impulse yorgas ypressureV waves -will be to a verylarge extent smoothed out by the action of the 'chambers of the mumer,and consequently, a much more uniform flow of gas will discharge fromthe tail pipe, and consequently, objectionable noises ordinarily causedby the discharge of gases from. the end of the tail pipe 'into theatmosphere will be eliminated.A Inaddition to the alternating flow ofgases into andv outof the chambers, there will be a more or lessconstant now through these chambers in the general direction toward thedischarge end' of the muiller, ,which ow results in the drawing of thefcooled gases, back into the innershell for mixture with' the hot gasesand for producing the rechambers.

fraction and absorption of sound waves in this shell. Without thiscontinuous 110W,` the cooled gases in the outer chambers would not bemixed to any appreciable extent with the gases in the inner shell, sincethese cooled gases would act more or less as buffers or cushions in theouter chambers without actually passing out of these 'Ihe passing ofgases through the chambers about the inner shell also reduces the volumeof gases whichl must pass through the in-l ner shell and, consequently,reduces back pressure in the muilier. I have found it particularlyeiective in silencing the exhaust to provide imperforate bailles andpassing the gases in opposite directions into and out of an outerchamber through apertures in the inner shell.A

It will be understood that the`constructions shown in the drawing aremerely illustrative of theprinciple of my linvention and numerouschanges in'the details of construction may be made. I While the bestresults are obtained when the inner shell is of lesser diameter at itsdischarge end than at its receiving end, yet I have found that incertain cases good results can be obtained if the inner shell is ofuniform diameter throughout, if other meansare employed vfor slightlyreducing the pressure near the discharge end of the muiiler.

I claim as my invention:

l.' A muiller havinginlet and outlet openings, an inner perforate shellextending from said inlet toward Lsaid outlet opening, intermediate andouter shells arranged concentrically about said inner shell, bailieslconnectingsaid inner and intermediate shells and dividing the spacebetween Y said inner and'intermediate shells into a plurality ofturbulence chambers, a baffle extending from lessen the intensity ofsounds emitted by the A muiiler.

2. A muiiler includingv inner, intermediate, and

outer shells, the inner shell vbeing perforate and forming asubstantially direct passage through said muier, said inner andintermediate shells forming between themv an inner chamber, theperforations in said inner shell establishingcommunication between theinterior thereof and said inner chamber, an outer chamber formed betweensaid intermediate and outer shells, and substan- `tially imperforatebaiiies disposed crosswise of said shells and subdividing the Vinner'chamber into separate turbulence chambers and said outer chamberi'ntocooling compartments, said intermediate shell being perforatesolely in limited minor zones, with the perforations connecting cachouter cooling compartment through one-of said zones with one of saidturbulence chambers and throughanother of said zoneswith another v ofsaidI turbulence chambers, said perforations also connecting one of saidturbulence chambers with both of said cooling compartments whereby gasesmay enter eachcooling compartment from through said muiller, and beingformed of portions of varying diameters, the portions ofl said innershell nearer to the discharge end of said muiilerbeing of less diameterthan the portion near the gas receiving end of said inner shell, saidintermediate and inner shells forming between them a sound eliminatingchamber, a plurality of imperforate, transverse baille means disposedacross said chamber at intervals along its length and subdividing itinto' turbulence chambers, the space between said intermediate and outershells forming a cooling chamber, imperforate partition means disposedacross said cooling chamber at a point between two of said baffle meansto subdivide said cooling chamber into compartments, said intermediateshell having a periorate zone connecting one end portion of eachcompartment to one turbulence chamber and another perforate zoneconnecting the other end portion of that compartment to anotherturbulence chamber, said intermediate shell being otherwisesubstantially imperforate.

4. A muiller including an inner shell and intermediate and outer shellsarrangedabout said inner shell, the space between the intermediate andouter shells forming a cooling chamber, means cooperating with saidshells to divide the space between said inner and intermediate shellsinto a plurality of non-communicating intermediate chambers, imperforatemeans disposed transversely across saidcooling chamber and dlviding itinto compartments disposed end to end, said inner shell communicatingdirectly with y each of said intermediate chambers, and passages in saidintermediate shell solely in zones thereof spaced substantially apartlengthwise of that shell for connecting each cooling compartment atdiierent zones thereof directly with two adjacent intermediate chambers,one' of which intermediate chambers is connected to both of saidcompartments, said passages having an aggregate area which is verymaterially less than the area of communication between said inner shelland said intermediate chambers.

5. A muffler having inlet and discharge openings in opposite endsthereof, an inner shell open at its opposite ends and extendingsubstantially from the inlet to the discharge opening of said muiiler,said shell being provided with perforations substantially throughout thelength thereof and being of smaller diameter at the discharge endthereof than at the inlet end, intermediate and outer shells arranged inspaced relation to each other about said inner shell, means for closingthe ends of the spaces between said inner, intermediate and outershells, imperiorate bailles arranged between said inner and intermediateshells and forming a plurality'ofv intermedate chambers disposed endtoend, an imperforate wal arranged between and connecting the intermedateand outer shells at a point between two intermediate bailles in adirection along the length of the shells and dlvidimr the space betweensaid intermedate and outer shells into outer chambers disposed end toend, each outer chamber being arranged in overlapped relation to the twoadjacent intermediate chambers, and perforatio'ns in said intermediateshell to establlish communication of each outer chamber with the twoadjacent intermediate chambers, one of said intermediate chambersestablishing communication between the two outer chambers separatelyfrom the passage through the inner shell.

6. A muiiier having inlet r`and outlet openings, an inner perforateshell extending from said inlet toward said outlet opening, intermediateand outer shells arranged concentrically about said inner shell, aplurality of substantially imper-V forate baiiles connecting said innerand intermediate shells and dividing the space between said inner andintermediate shells into a plurality of chambers, a substantiallyimperforate wall extending from said intermediate to said outer shell ata point between two of said ballles, andA dividing the space betweensaid intermediate and outer shels into separate compartments having nodirect communication with one another, said intermediate shell beingapertured solely in relatively small zones spaced apart along tne lengthof said intermediate shell but with said zones at opposite sides of eachof said bailles connecting said inner and intermediate yshells andconnecting each intermediate chamber directly with two different andadjacent compartments, and each compartment with two different andadjacent chambers.

7. A muiller including inner, intermediate, and outer shells, the innershell being perforate and forming a substantially direct passage throughsaid muiller, said inner and intermediate shells forming lbetween theman inner chamber, the perforations in said inner shell establishingcommunication between the interior thereof and said inner chamber,separate and non-communicating outer compartments formed between saidintermediate and outer shells and disposed in a row along the length ofsaid outer shell, and substantially imperforate bailies disposedcrosswlse of said inner and intermediate shells, each at a point betweenthe ends of an adjacent compartment, and subdividing said inner chamberinto separate non-communicating lsub-chambers, each overlapping with'anadjacent compartment, said intermediate shell being perforate solely inlimited minor z'ones spaced apart in a direction endwis'e of the shells,with each outer compartment communicating directly through one of saidzones with one of the inner sub-chambers, and through another of saidzones with another of said subchambers, and with each sub-chamberbetween the `end sub-chambers communicating directly with a plurality ofadjacent compartments, the total areas of the perforations in the zoneof the intermediate shell leading to one inner subchamber from onecompartment being less than for the zone leading from the samecompartment into another inner sub-chamber.

8. A muiller for internal combustion engines and the like comprising acasing subdivided by imperforate walls into a direct passagetherethrough from end to end, and a plurality o! separate chambers, onevgroup of said chambers being disposed along and communicating directlyand freely with said direct passage, but' having substantially no directcommunication with one another, and another group of said chambers beingdisposed along the chambers of said one group and having substantiallyno direct communication with one anothen'each of the chambers of said,another group having restricted direct communication with two diil'erentchambers of said one group, and at least one chamber oi said one grouphaving direct communication separately of the other chambers of thatgroup and of said passage, with a plurality of the chambers of saidanother group, whereby t e chambers of said another group may allcommunicate with one aning disposed along ,and communicating directlyIand freely with said direct passage, but having substantially no directcommunication with one another, and another group of said chambers bejing disposed along the chambers of said one group and havingsubstantially no direct communication with one another, each of thechambers of said another group having restricted` direct communicationwith two different chambers of said one group, and at least one chambero f said one group havingdirect communication separately of the otherchambers of that group and of said passage, with a plurality of thechambers o! saidanother group, whereby the /chambers of said anothergroup may all communicate with f one another through the chambers ofsaid one group, so asA to provide for restricted and local communication4between chambers of said one group by means of a chamber 'of saidanother group, some of the chambers of said one group having differentvolumes; A

10. A muiller for internal combustion engines and the` like comprising acasing subdivided by imperforate walls into a direct passagetherethrough from end to end, and a plurality of separate'ch'ambers, onegroup of said chambers being disposed in a rowalong and communicatingdirectly and freely with said direct passage, but

having substantially no direct communication withUone another, andanother group-of said' chambers being disposed along the chambers ofsaid one group and having substantially no direct communication with oneanother, each of the chambers of said another group having restrictedcommunication, solely at kzones spaced substantially apart ln adirection lengthwise ofl said direct passage, with two chambers of saidone group, and each intermediate chamber in said row of said one grouphaving restricted communication with two f the chambers of said anothergroup solely at said zones. so as to provide for restricted and localAcommunication between chambers of said one group by means of a chamberor said another group.

11. A munier for internal combustion engines and the like comprising acasing subdivided by imperforate walls into a dirct passage therethroughfrom end to end, and a plurality of sep'- arate chambers, one group ofsaid chambers being disposed in a row along and communicating 'directlyand freely with said direct passage, but

having substantially no' direct communicationwith one another, andanother group of said chambers being disposed in a -row along theVchambers of said one group and having substantially noYdirectcommunication with one another, each of the chambers of saidanother group having restricted /communication, solely at zones spaced.substantially apart in a direction length-v wise et said directpassage, with two chambers of said one group, and each intermediatechamber in said row'o! said one group having re- Aaos-4,186

stricted communication with two of the chambers yof said another groupsolely at said zones, so as to provide for restrictedV and localcommunication between chambers of said one group by means of a chamberof said another group, the aggregate areas of communication between eachchamber of said another group with the chambers of said one group, beinggreater at' the zone nearer the inlet end of said direct passage than atthe other zone of the same chamber of said another group.

12. A muiier having inlet and outlet openings, an inner perforate shellextending from. said inlet toward said outlet opening, intermediate andouter shells arranged concentrically about said inner shell, baiiiesconnecting said inner and intermediate shells and dividing the spacebetween said inner and intermediate shells into a plurality of chambers,a wall extending from said intermediateto said outer shell,approximately mid` way between the two nearest battles and dividing thespace between said intermediate and outer j shells into separatechambers, perforations in said intermediate shell at opposite sides ofeach of said baiiles connecting said inner and intermediate shells, atleast one of said inner chambers between said inner and intermediateshells receiving cool gases from one of said outer chambers anddischarging gases to said other outer chamber through said perforationsin said intermediate shell, and also being arranged to receive hot gasesthrough the perforations of said inner shell, to set up a'turbulence ofgases within said intermediate chamber to retract sound waves.

13. A, muler including inner, intermediate and outer shells, said innershell being perforate and through said manier, and being formed ofportions of varying diameters, the portion of said inner shell nearer.to the discharge end of said muiiier being of less diameter than theportion f near the gas receiving .end of said inner shell,v saidintermediate and inner shells forming beforming a substantially directpassage for gases tween them asound eliminating chamber, im-

sage, the space between said intermediate and.v

outer shells forming a cooling chamber, an im- -perforate wallconnecting the outer and intermediate shells at a point intermediatesaid baille means and dividing said cooling chamber intov compartmentsdisposed end to end lengthwisel l along said shells, with eachcompartment overlapping with a common turbulence chamber with which the'other compartment overlaps, said interlmediate shell having perloratezones to provide lcommunication from said common turbulence perforatezones of said intermediate shell having a less aggregate perforate areathan the asgref gate perforate areas oi the section oi' said passagethrough those turbulence chambers, and the aggregate perforate area ofthe zone connecting said common chamber to the compartment nearest thegas inlet end of said passagebeing greater than f orthe zone connectingsaid common chamber to the othercompartment, substantially all of thegases'from said chambersbeing returned LAURENCE R. HEATH.

to said inner shell for `discharge from said muiier."

